The present invention relates to a device for controlling the ignition timing of an engine with the pressure within the cylinder.
Devices for electronically controlling the ignition timing of an automotive gasoline engine to improve the engine output, response, and exhaust are known. The practical devices make use of the output of an air flow meter or the pressure within the intake pipe as engine load information for calculating the ignition timing. Of these two systems, the air flow meter system is high in measuring precision but expensive. The intake pressure detection system, on the other hand, is relatively inexpensive but lower in measuring precision than the air flow meter system.
A conventional intake pressure detection system is shown in FIG. 7. There is provided a throttle valve 3 in the intake passage 2 of an engine 1. At the downstream from the throttle valve 3 there is provided a surge tank 2a which is equipped with a pressure sensor 4. An injector 5 is mounted on the intake passage 2 to inject a fuel toward a combustion chamber 12. At the upstream therefrom there is provided an intake temperature sensor 6 for detecting the intake temperature within the intake passage 2. A spark plug 7 is mounted on the combustion chamber 12 and connected to an ignition coil 9 via a distributor 8. The ignition coil 9 and the injector 5 are controlled by a computer unit 11. A water temperature sensor 13 detects the temperature of a coolant for the engine 1. A rotation sensor 14 picks up the rotation signal of the engine 1.
The signal of the pressure sensor 4 is taken as a parameter indicative of the quantity of air charged into the combustion chamber 12. This signal is corrected with the signal of the intake temperature sensor 6 and then the correction factor which has been measured with respect to the charge efficiency which varies with the engine speed and the load and stored in a read only memory (ROM) for use as an engine load. The ignition timing is determined based on the map value which is related to the above engine load and the engine speed, and an ignition signal is outputted to the ignition coil 9.
In the conventional, inexpensive intake pressure detection system, the quantity of air charged into the combustion chamber 12 is detected indirectly based on the intake pressure so that when the charge efficiency changes due to the operation timing of the intake and exhaust valves and the engine speed, the detection precision of the quantity of air or engine load is very low. In addition, the operation of the intake valve gives rise to pulsation in the intake passage 2 so that there is a time lag for averaging the detected signals, resulting in the poor response.